A medium voltage circuit breaker is a key component of a power plant, that is called to operate under different conditions, for example frequently switching load condition and very rarely under fault condition.
One of the most important key point for the system and for the customers is its reliability. A correct approach is going towards monitoring and diagnostic functions, that allows predicting system malfunction, scheduling preventive maintenance reducing impact on the supplied network and/or process.
In the state of the art, it is well known to use redundant switches in parallel, in order to take care of a safe switching operation. In DE 42 09 167 A1 is disclosed a semiconductor switch in parallel to a circuit breaker.
A further problem is, that even if in some cases, the diagnostic can be really advanced, there could be some limitation on this approach.
It is very difficult to perform a diagnostic so deep, especially in standard circuit breaker, to be able to check the full integrity of the apparatus.
This limitation is present in both, the main technologies used today with different way—magnetic actuator and mechanics actuator—because both systems are bistable.
This implies, that in order to test really the Open functionality of the actuator, it is needed to open the circuit breaker, and in order to test the Close functionality, it is needed to Close the circuit breaker.
Often, especially if the circuit breaker is used as protection and not as Load Switch in the process, it is rarely operated. This condition reduces deeply the possibility to capture data related to the status apparatus, for example switching time, travel curve and so on, because the breaker can't be opened in order to test that in case of failure it will Open the circuit.
One alternative approach can be, to perform redundancies in the power plant, having different level of protections, in different circuit breaker, coordinated between them. This approach, even if effective, leads to very high costs, engineering and space requirement.